1896.] NATURAL SCIENCES OF PHILADELPHIA. 235 



of interpretation of the facts of morphology." In another place, an 

 address entitled " Dynamics in Evolution," 1893, he said, " experi- 

 mental investigations in embryology will make no solid progress 

 until the mischievous influence of such speculations have been eradi- 

 cated from the minds of the present generation." These opinions 

 remained unmodified to the day of his death. Perhaps the best ex- 

 pression of his views can be found in a lecture delivered at "Wood's 

 Hole, 1894, and a second lecture entitled "A Dynamical Hypothe- 

 sis of Inheritance." 



The last phase of his scientific life is the most instructive, namely, 

 that relating to the application of geometry and the differential cal- 

 culus to the study of organic forms. The idea that anatomy and 

 mathematics can be of mutual assistance generally comes to savants 

 too late for practical use. Against the example of Helmholtz we cite 

 many failures. Mathematics came to John Goodsir too late for 

 anatomy, and anatomy to Fechner too late for mathematics. When 

 Ryder saw the necessity of preparing himself in these sciences 

 (for his early training had excluded them), he set to work to supply 

 the defect with characteristic energy. He studied geometry and the 

 calculus in spare hours. He became enthusiastic for them. He 

 declared geometry to be the noblest of the sciences. He read the 

 writings of Lord Kelvin carefully ; his admiration for them was 

 unbounded. At the time of Ryder's death, two works lay on the 

 bed, one was a text-book on the diflferential calculus, the other a 

 volume of Lord Kelvin's works. 



It is difficult to fix a time when the mathematical explanation of 

 the mechanics of evolution occurred to him. We have seen that he 

 was influenced by Haughton as early as 1874. If we can draw an 

 inference from the reading of the paper entitled " The Fore and Aft 

 Poles of Volvox mi)ior," previously quoted, and again the essay 

 " The Polar Differentiation of Volvox minor " and " Specialization of 

 Possible Anterior Sense Organs" (No. 174, Bibliography), the idea 

 apparently suggested itself by studies in the early Academy days on 

 the infusoria and later on the development of simple organisms. 

 The same conception occurs in his papers on " Energy in Biological 

 Evolution ; " " Of the Representation of the Relative Intensity of the 

 Conflict Between Organisms ; " " Energy as a Factor in Organic 

 Evolution ; " " Mechanical Genesis of the Form of the Fowl's Egg ; " 

 " The Adaptive Forms and Vortex Motions of the Substance of the 

 Red Blood Corpuscles of Vertebrates ; " " The Correlation of the 



